This invention relates to safety terminals for controlling the internal pressurization and/or electric circuit of an electrochemical cell which under some conditions produces excessive gas pressure upon being electrically driven.
Sealed casings hereto provided for electrical devices, such as rechargeable nickel-cadmium batteries and other electrical devices which may, from time to time generate gases within the sealed container, have included safety vents for releasing or venting gases at abnormal pressures. The use of a rupturable diaphragm to release internal gas pressure is old as shown for example by U.S. Pat. No. 3,214,300. Use of a ball valve in a battery pressure relief device is illustrated in U.S. Pat. No. 3,497,396, and a resilient deformable ring device used in a battery venting system is described in U.S. Pat. No. 3,497,395.
A Li/SO.sub.2 cell normally has SO.sub.2 gas under some pressure. If such a cell is overdischarged a violent explosion can result from the excessive pressure. It is desirable to disconnect the battery from the electrical circuit prior to a hazardous overpressure condition developing due to extended discharge (or overcharge for secondary type cells). Current technology requires a pressure transducer, control circuitry and circuit relays to sense the excess pressure and disconnect the circuit.